Trailer Hitch Wiring Question

[fourD2]

I had UHaul put a trailer hitch on my car a short while back.  The technician who put the hitch on did not hook up the wiring harness because he was not trained up enough to do that.  I had not planned to pull a trailer anyway, it was for a hitch mounted bicycle rack so I let it go at that.

I now would like to hook up the wiring harness as there are occasions when I need to pull a small utility trailer.  The Subaru dealer where I purchased the car indicated they would not do the electrical hook up (or the hitch for that matter as I had originally gone to them for that job). 

There is a Trailer sales company nearby that indicated they would do it but the quote for the work was around $325 which I thought was a bit high, more than what I paid for the trailer hitch installation.

I think I can do the Plug-and-Play electrical part myself except for running the wire up front to the 12 Volt battery.  That looks tricky and requires a hoist.

My question is:  If I just plug the 12V wire into a portable 12V battery placed in the trunk when I want to pull a trailer, can I disconnect the wire when not in use?  In other words, will the car’s tail lights work normally if the 12V wire that runs the trailer lights is disconnected?

[jmilks]

This option should work but you will have to ground the negative terminal of your secondary trunk battery to the chassis so that the two battery grounds are tied together.

[fourD2]

Thank you.  There is a ground wire in the harness.  Is there any reason the ground wire that comes off the negative pole of the secondary 12 V battery and the harness ground wire cannot be affixed to the same chassis bolt.  Just trying to keep the wiring tidy.

[jmilks]

yes that is exactly what I would do.